In the oil and gas exploration and production industry there are many occasions where seals of varying configurations must be established downhole. For example, seals may be required within an annulus defined between, for example, concentric tubulars, between a tubular and a bore wall, or the like. Such seals may be achieved by use of mechanical actuators which physically set, and in some occasions release sealing members at the desired location. However, there are inherent reliability concerns associated with any downhole mechanical assembly in view of the significant difficulties and costs associated with recovering a failed assembly and implementing appropriate remedial measures.
It has been proposed in the art to establish seals in downhole annular locations using materials which swell upon contact with a particular activator, such as water, hydrocarbons or the like. Generally, the swellable material, such as a swelling elastomer, is positioned in an annular space, for example between a tubing string and a bore wall, and then subsequently permitted to swell, for example upon contact with ambient fluids, to fill the annular space and establish the necessary seal. The swellable material is normally mounted and bonded to the exterior surface of conventional wellbore tubulars, such as casing tubulars, liner tubulars, production tubulars and the like. However, this arrangement requires the conventional tubulars to be modified, or specially manufactured, which may increase operation costs and cause delays to wellbore operations.
It has also been proposed in the art to provide a swelling material on a separate sleeve which may subsequently be mounted on the required wellbore tubular. However, an appropriate seal between the sleeve and the tubular must be established to prevent migration of fluids past the sleeve. Conventional sealing arrangements may include o-ring seals and the like which may not provide the necessary sealing integrity, especially when exposed to extremely large pressure differentials. Additionally, conventional seals, such as o-rings, may be damaged or displaced when the sleeve is mounted on the tubular.